In order to reduce the number of accidental poisonings resulting from young children having access to unsafe medicines, drugs, household chemicals and other products, there has been considerable activity in recent years toward the development of closures and containers in which a type of manipulation between the cap and container is required in order to gain access to the contents of the container that a young child is incapable of performing. For example, it has been found that young children are generally incapable of manipulating a cap mounted on a container with bayonet-type locking means-- a type of locking means that requires that the cap be pushed axially relative to the container and then rotated relative to the container in order to separate the cap from the container. The cap must be pushed axially toward the container against the biasing force of a spring in order to disengage the bayonet locking means. See, for example, Hedgewick U.S. Pat. No. Re. 27,156. Other examples of safety closure and container assemblies having various locking and sealing arrangements are disclosed in U.S. Pat. Nos. 2,776,066; 3,445,022; 3,608,763; 3,623,623; 3,669,294; 3,675,804; 3,739,933; 3,741,421; 3,888,376; 3,794,200; 3,952,899; 3,963,139; 3,979,001; 4,032,028; and 4,049,148.
When the contents of the container is liquid, or is some substance that deteriorates in an atmosphere of high humidity, the closure must be capable of maintaining an adequate seal under a variety of conditions. The contents of the container, if liquid, may require vigorous shaking before being used, or the contents may be of the type that causes a pressure buildup within the container over a period of time. A tight seal is also necessary in order to prevent the undesired escape of the contents from the container, and because the entrance of moisture and other contaminants into the container may cause deterioration of the contents.
In order to maintain a good seal against the entrance or escape of moisture, it is desirable to be able to provide a seal that projects into the mouth of the container and engages the inner surface of the container mouth with a tight fit. While the spring force on the cap should be sufficient to prevent children from gaining access to the contents, it should not be so great as to make unduly difficult for adults to manipulate the cap. Accordingly, a tight seal must be maintained by the closure without at the same time making it too difficult for adults to manipulate the closure.
In order to provide a tight, moisture proof seal, it is generally necessary for the cap to carry a sealing member with a flange that projects into the mouth of the container into tight, sealing engagement with the inner surface thereof. U.S. Pat. Nos. 3,432,065; 3,623,623; 3,753,510; 3,974,928; and 4,049,148 each disclose safety closure and container assemblies having sealing members that are pushed into the mouth of the container by dome-shaped spring portions on the sealing members. Considerable force is required in order to insert and remove such sealing members from the mouth of the container. With conventional bayonet locking elements on the cap and container of the type shown in the patents referred to in the preceding paragraph, the seal is inserted into and removed from the container primarily by the application of direct axial force between the cap and container. The operator, in applying the cap to the container, must first exert considerable axial pressure between the cap and container in order to force the seal into the mouth of the container before the cap is rotated into locked engagement with the container. Conversely, in order to remove the cap from the container, after the cap has been unlocked from the container, the operator must pull the cap and seal axially from the container with a force sufficient to overcome the resistance of the seal to disengagement from the container. For the aged, arthritic or otherwise infirm user, the force required can cause considerable inconvenience.